1. Field of the Invention
The present invention relates generally to traffic detection and monitoring equipment. In particular, the present invention is a vehicle detection system in which infrared or visible images of highway/street scenes are processed by digital computing means to determine vehicle presence, passage, measure various traffic parameters and facilitate traffic surveillance and control. The system also can be used as a vehicle counter/classifier, and other traffic engineering applications such as incident detection, safety analysis, measurement of traffic parameters, etc.
2. Description of the Prior Art
Traffic signals are extensively used to regulate the flow of traffic at both high volume urban intersections, and rural or suburban low volume intersections where safety rather than capacity and efficiency is the major concern. The timing of traffic control signals (i.e., the cycle time and amount of green provided to each movement) is either fixed through the use of historical data, or variable and based upon real-time sensed data. Timing sequences of pretimed traffic control signals are derived from historical information concerning the demand patterns, while real-time traffic control decisions are derived from actual traffic flow information. This information can be processed locally, or remotely-transmitted to a central computer where decisions about signal settings are made. Real-time traffic control signals have the ability to respond to rapid demand fluctuations and are in principle more desirable and efficient than pretimed signals.
Currently used equipment for real-time control of traffic signals is expensive and often inaccurate. Effective traffic sensing for surveillance and control of freeways and arterial streets requires vehicle detection, counting, classifying and other traffic parameter measurements. The overwhelming majority of such detectors are of the inductive loop type, which consist of wire loops placed in the pavement to sense the presence of vehicles through magnetic induction. Since the information extracted from such detectors is very limited, installation of a number of such detectors is often required to obtain requisite data for sophisticated traffic control and surveillance systems. For example, measurements of traffic volume by lane require at least one detector per lane, while measurement of speed requires at least two detectors. A problem with existing systems is reliability and maintenance. In major cities 25%-30% of inductive loops are not operational. In addition, inductive loops are expensive to install.
Electro-optical vehicle detection systems which utilize visible or infrared sensors have been suggested as a replacement for wire loop detectors. The sensor of such systems, such as an electronic camera, is focused upon a field of traffic and generates images at predetermined frame rates (such as standard television). Under computer control, frame data with traffic images is captured, digitized, and stored in computer memory. The computer then processes the stored data. Vehicle detection can be accomplished by comparing the image of each selected window with a background image of the window in the absence of vehicles. If the intensity of the instantaneous image is greater than that of the background, vehicle detection is made. After detection, the vehicle's velocity and signature can be extracted. From this, traffic data can be extracted and used for traffic control and surveillance.
In order for electro-optical vehicle detection systems of this type to be cost effective, a single camera must be positioned in such a manner that it covers a large field of traffic so that all necessary information can be derived from the captured image. In other words, one camera must be capable of providing images of all strategic points of an intersection approach or of a roadway section from which it is desired to extract information. The time required by the computer to process frames of these images is very critical to real-time applications. Furthermore, currently used methods for processing the data representative of the images are not very effective.
It is evident that there is a continuing need for improved traffic control and surveillance systems. To be commercially viable, the system must be reliable, cost-effective, accurate and perform multiple functions. There is a growing need for controlling traffic at congested street networks and freeways. This can only be accomplished through real time detection and surveillance devices. Such a machine-vision device is proposed here. The ultimate objective is to replace human observers with machine-only vision for traffic surveillance and control. Finally, the proposed device increases reliability and reduces maintenance since it does not require placement of wires to the pavement.